# discrete random variable second equationWatch

Thread starter 9 years ago
#1
The random variable X has probability distribution
x 1 3 5 7 9
P(X = x) 0.2 p 0.2 q 0.15
(a) Given that E(X) = 4.5, write down two equations involving p and q.

the first equation is quite easy as i just know that P(X = x) = 1
so 0.2 + p + 0.2 + q + 0.15 =0.55

this would mean 0.55 -1 = 0.45
so p+q = 0.45

im cnt think of any other equation? could anyone suggest something please?
0
quote
9 years ago
#2
You need to use E(X) somehow. E(X) = "", i.e. the sum of the products of x and its associated probability.

Spoiler:
Show
1 * 0.2 + 3p + 5*0.2 + 7q + 9*0.15 = E(X) = 4.5
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